As is known, an electrode for electroerosive cutting can be a thin wire having a diameter which lies in the range of 0.02 to 0.35 mm. During the cutting process the wire is unwound from a supply bobbin. Within a complicated mechanism which is located above and beneath the workpiece, the wire electrode is deviated and tensioned. The tension may be for example, 16 Newton. Furthermore diamond and sapphire guides for strictly maintaining the position of the wire electrode are provided in the mechanism and, in particularly during conical cutting, apply high friction to the wire electrode so that the latter is tensioned up to its tensile strength.
The working current which is up to several hundred amperes per pulse at repetition frequencies of up to 250 kHz, is applied to the thin wire electrode by means of thin wiper contacts. The transition areas for the working current are very small. Due to the rise in temperature as a result of the high working current the areas in the dielectric insulator in which the specific erosion process between the workpiece and the wire electrode takes place must be cooled. The disadvantage of this cooling is that the areas for the current transition are subjected to electroerosion, too, which leads to their early destruction.
In addition, the areas for the current transition increase the friction on the wire electrode. During the erosion process the known wire electrode is adversely affected by the following forces in the working gap: electrostatic forces, spark discharge forces as well as mechanical forces arising from the flow of the dielectric fluid and from gas bubbles. These forces in the working gap create undesirable vibrations of the wire electrode which lie in the range of the natural frequency of the tensioned wire electrode of approximately 1 kHz. This lowers the efficiency of the erosion process by a factor of 2 to 3. A further disadvantage resides in the fact that on the known wire electrode material is removed in an undesirable manner (electrode wear) due to the spark discharge in the working gap. This leads to an additional reduction of the diameter of the thin wire electrode. This disadvantage cannot even be compensated by a higher feed velocity of the wire electrode because that velocity is greatly restricted by the characteristics of the material such as, for instance, the elasticity modulus of the wire electrode.
In addition the wire electrode, already stressed to its limit by the above mentioned effects, will be torn apart by unpredictable troubles in the erosion process, e.g. short circuits and arc discharges.